U.S. patent number 8,599,912 [Application Number 12/582,523] was granted by the patent office on 2013-12-03 for apparatus and method for channel estimation in mobile communication system.
This patent grant is currently assigned to Samsung Electronics Co., Ltd.. The grantee listed for this patent is Sung-Wook Kang, Young-Min Ki, Hun-Kee Kim. Invention is credited to Sung-Wook Kang, Young-Min Ki, Hun-Kee Kim.
United States Patent |
8,599,912 |
Ki , et al. |
December 3, 2013 |
Apparatus and method for channel estimation in mobile communication
system
Abstract
An apparatus and method for reducing power consumption of a
receiver of a mobile communication system are provided. The
apparatus includes an adaptive multi-tap segment channel estimator
for determining a segment size according to a delay spread value
for each channel tap, for determining a channel estimation
frequency by determining a sum of segment block energy, and for
allocating each segment to the channel estimator.
Inventors: |
Ki; Young-Min (Suwon-si,
KR), Kim; Hun-Kee (Seoul, KR), Kang;
Sung-Wook (Seoul, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Ki; Young-Min
Kim; Hun-Kee
Kang; Sung-Wook |
Suwon-si
Seoul
Seoul |
N/A
N/A
N/A |
KR
KR
KR |
|
|
Assignee: |
Samsung Electronics Co., Ltd.
(Suwon-si, KR)
|
Family
ID: |
42108649 |
Appl.
No.: |
12/582,523 |
Filed: |
October 20, 2009 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20100098145 A1 |
Apr 22, 2010 |
|
Foreign Application Priority Data
|
|
|
|
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Oct 20, 2008 [KR] |
|
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10-2008-0102458 |
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Current U.S.
Class: |
375/232; 375/316;
375/259; 370/352; 375/346; 370/210; 375/343; 370/236 |
Current CPC
Class: |
H04L
25/0212 (20130101); H04B 1/7113 (20130101); H04B
2201/70701 (20130101) |
Current International
Class: |
H03H
7/30 (20060101) |
Field of
Search: |
;375/232,316,329,260,343,246,332,346 ;370/210,236,352 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Vlahos; Sophia
Attorney, Agent or Firm: Jefferson IP Law, LLP
Claims
What is claimed is:
1. An apparatus for channel estimation in a mobile communication
system, the apparatus comprising: an adaptive multi-tap segment
channel estimator configured to divide a channel tap region within
a channel to be estimated into a plurality of segments, configured
to determine a channel estimation frequency and a segment size for
each of the plurality of segments, and configured to allocate each
of the plurality of segments to the adaptive multi-tap segment
channel estimator, wherein the adaptive multi-tap segment channel
estimator regulates the channel estimation frequency according to
each segment's energy.
2. The apparatus of claim 1, wherein the adaptive multi-tap segment
channel estimator determines a delay spread value by determining
time average power for each of the plurality of segments to
determine a segment size for each of the plurality of segments in
such a manner that, if the delay spread value is small, the segment
size comprises a small size, and if the delay spread value is
large, the segment size comprises a large size.
3. The apparatus of claim 2, wherein the delay spread value
comprises a Root Mean Square (RMS) delay spread.
4. The apparatus of claim 1, wherein the adaptive multi-tap segment
channel estimator determines a sum of energy for each of the
plurality of segments and determines the channel estimation
frequency by using the determined energy sum and a Doppler
level.
5. The apparatus of claim 1, wherein the adaptive multi-tap segment
channel estimator regulates a hardware usage rate according to the
channel estimation frequency.
6. The apparatus of claim 5, wherein the adaptive multi-tap segment
channel estimator determines segment mapping information to perform
mapping to a hardware segment.
7. The apparatus of claim 5, wherein the adaptive multi-tap segment
channel estimator determines a hardware occupancy rate at the
channel estimation frequency to regulate the hardware usage rate in
such a manner that, if an unused hardware segment is detected by
using the hardware occupancy rate, at least one of a neighbor tap
region and another channel is searched for by using the unused
hardware.
8. The apparatus of claim 7, wherein the adaptive multi-tap segment
channel estimator determines a hardware occupancy rate at the
channel estimation frequency to regulate the hardware usage rate in
such a manner that, if a hardware occupancy rate is less than a
predefined threshold, segments with a low hardware occupancy rate
share hardware segments to reduce hardware size and power
consumed.
9. A method for channel estimation in a mobile communication
system, the method comprising: dividing, by an adaptive multi-tap
segment channel estimator, a channel tap region within a channel to
be estimated into a plurality of segments; determining a channel
estimation frequency and a segment size for each of the plurality
of segments; and allocating each of the plurality of segments to
the adaptive multi-tap segment channel estimator, wherein the
channel estimation frequency is regulated according to each
segment's energy.
10. The method of claim 9, wherein the determining of the segment
size for each of the plurality of segments comprises: determining a
delay spread value by determining time average power for each of
the plurality of segments; and determining a segment size for each
of the plurality of segments in such a manner that, if the delay
spread value is small, the segment size comprises a small size, and
if the delay spread value is large, the segment size comprises a
large size.
11. The method of claim 10, wherein the delay spread value
comprises a Root Mean Square (RMS) delay spread.
12. The method of claim 9, wherein the determining of the channel
estimation frequency comprises: determining a sum of energy for
each of the plurality of segments; and determining the channel
estimation frequency by using the determined energy sum and a
Doppler level.
13. The method of claim 9, further comprising regulating a hardware
usage rate according to the channel estimation frequency.
14. The method of claim 13, further comprising determining segment
mapping information to perform mapping to a hardware segment.
15. The method of claim 13, wherein the regulating of the hardware
usage rate comprises: determining a hardware occupancy rate at the
channel estimation frequency; and regulating the hardware usage
rate in such a manner that, if an unused hardware segment is
detected by using the hardware occupancy rate, at least one of a
neighbor tap region and another channel is searched for by using
the unused hardware.
16. The method of claim 15, wherein the regulating of the hardware
usage rate further comprises that, if a hardware occupancy rate is
less than a predefined threshold, segments with a low hardware
occupancy rate share hardware segments to reduce hardware size and
power consumed.
Description
PRIORITY
This application claims the benefit under 35 U.S.C. .sctn.119(a) of
a Korean patent application filed in the Korean Intellectual
Property Office on Oct. 20, 2008 and assigned Serial No.
10-2008-0102458, the entire disclosure of which is hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an equalizer-based receiver in a
mobile communication system. More particularly, the present
invention relates to an apparatus and method for reducing power
consumption of the receiver by decreasing a multi-tap size in an
equalizer-based receiver in a mobile communication system.
2. Description of the Related Art
With recent standardization and commercialization of a mobile
communication system that requires high-rate data transmission,
such as a Wideband Code Division Multiple Access (WCDMA), High
Speed Downlink Packet Access (HSDPA), and the like, research is
presently conducted for an equalizer-based receiver suitable for
high-rate data reception.
A conventional equalizer-based receiver includes an equalizer and a
multi-tap channel estimator having a tap long enough to
sufficiently receive a delay profile of a reception channel. The
multi-tap with a sufficiently long length is designed where a
multi-path reception channel has a long delay profile. However, in
an actual channel reception environment, the multi-path reception
channel does not always have the long delay profile.
Therefore, in a conventional method, the multi-tap with a long
length is selectively used according to a channel environment
without having to use all multi-taps. That is, a receiver estimates
a delay profile of a received signal according to a multi-path to
lock only a necessary tap among the multi-taps, and receives a
signal by unlocking the remaining taps. The method of using the
necessary tap by locking only the necessary tap can reduce power
consumption since hardware elements are less used in certain
situations and can remove performance deterioration caused by noise
when a tap not having multi-path energy is locked.
Although the multi-tap with a long length is designed where the
multi-path reception channel has a long delay profile, there is a
decreased probability that the multi-path reception channel
actually has such a long delay profile.
Accordingly, a channel estimator for guaranteeing performance of a
receiver will have a long tap and hardware elements of the channel
estimator will operate with a sufficiently long tap.
Therefore, a need exists for an equalizer-based receiver in a
mobile communication system with a decreased multi-tap size for
reducing hardware size and power consumption.
SUMMARY OF THE INVENTION
An aspect of the present invention is to address at least the
above-mentioned problems and/or disadvantages and to provide at
least the advantages described below. Accordingly, an aspect of the
present invention is to provide a method and apparatus for
operating an equalizer-based receiver in a mobile communication
system.
Another aspect of the present invention is to provide a method and
apparatus for reducing hardware complexity by decreasing a
multi-tap size in an equalizer-based receiver of a mobile
communication system.
Still another aspect of the present invention is to provide an
apparatus and method for determining a channel estimation rate
according to a multi-tap size in a mobile communication system.
Yet another aspect of the present invention is to provide an
apparatus and method for performing an operation in a search mode
for a neighbor tap or another channel according to a hardware
occupancy rate in a mobile communication system.
In accordance with an aspect of the present invention, an apparatus
for channel estimation in a mobile communication system is
provided. The apparatus includes an adaptive multi-tap segment
channel estimator for dividing a one-tap channel estimator into a
plurality of segments, for determining a channel estimation
frequency and a segment size for each channel tap, and for
allocating each segment to the channel estimator.
In accordance with another aspect of the present invention, a
method for channel estimation in a mobile communication system is
provided. The method includes dividing a one-tap channel estimator
into a plurality of segments, determining a channel estimation
frequency and a segment size for each channel tap, and allocating
each segment to the channel estimator.
Other aspects, advantages, and salient features of the invention
will become apparent to those skilled in the art from the following
detailed description, which, taken in conjunction with the annexed
drawings, discloses exemplary embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, features, and advantages of certain
exemplary embodiments of the present invention will be more
apparent from the following description taken in conjunction with
the accompanying drawings, in which:
FIG. 1 is a block diagram illustrating a structure of a receiver in
a mobile communication system according to an exemplary embodiment
of the present invention;
FIG. 2 is a block diagram illustrating a structure of an adaptive
multi-tap segment estimator of a receiver according to an exemplary
embodiment of the present invention;
FIG. 3 is a block diagram illustrating a structure of a multi-tap
segment estimator of an adaptive multi-tap segment estimator
according to an exemplary embodiment of the present invention;
FIG. 4 is a block diagram illustrating a structure of a Pseudo
random Noise (PN) generator of an adaptive multi-tap segment
estimator according to an exemplary embodiment of the present
invention;
FIG. 5 is a block diagram illustrating a structure of a channel
estimation controller of an adaptive multi-tap segment estimator
according to an exemplary embodiment of the present invention;
FIG. 6 is a block diagram illustrating a structure of a segment
controller of an adaptive multi-tap segment estimator according to
an exemplary embodiment of the present invention;
FIG. 7 is a flowchart illustrating a multi-tap lock control process
of a channel estimation controller in a receiver according to an
exemplary embodiment of the present invention;
FIG. 8 is a flowchart illustrating a slewing process using a
movement average in a receiver according to an exemplary embodiment
of the present invention;
FIG. 9 is a flowchart illustrating a segment control process of a
receiver according to an exemplary embodiment of the present
invention;
FIG. 10 is a flowchart illustrating a process of determining a
channel estimation rate in a receiver according to an exemplary
embodiment of the present invention;
FIG. 11 is a flowchart illustrating a process of performing a
channel search mode in a receiver according to an exemplary
embodiment of the present invention;
FIG. 12A illustrates a performance of a receiver according to the
related art;
FIG. 12B illustrates a performance of a receiver according to an
exemplary embodiment of the present invention; and
FIG. 12C illustrates a performance of a receiver according to an
exemplary embodiment of the present invention.
Throughout the drawings, like reference numerals will be understood
to refer to like parts, components and structures.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The following description with reference to the accompanying
drawings is provided to assist in a comprehensive understanding of
exemplary embodiments of the invention as defined by the claims and
their equivalents. It includes various specific details to assist
in that understanding but these are to be regarded as merely
exemplary. Accordingly, those of ordinary skill in the art will
recognize that various changes and modifications of the embodiments
described herein can be made without departing from the scope and
spirit of the invention. Also, descriptions of well-known functions
and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims
are not limited to the bibliographical meanings, but, are merely
used by the inventor to enable a clear and consistent understanding
of the invention. Accordingly, it should be apparent to those
skilled in the art that the following description of exemplary
embodiments of the present invention are provided for illustration
purpose only and not for the purpose of limiting the invention as
defined by the appended claims and their equivalents.
It is to be understood that the singular forms "a," "an," and "the"
include plural referents unless the context clearly dictates
otherwise. Thus, for example, reference to "a component surface"
includes reference to one or more of such surfaces.
By the term "substantially" it is meant that the recited
characteristic, parameter, or value need not be achieved exactly,
but that deviations or variations, including for example,
tolerances, measurement error, measurement accuracy limitations and
other factors known to those of skill in the art, may occur in
amounts that do not preclude the effect the characteristic was
intended to provide.
Hereinafter, exemplary embodiments of the present invention provide
an apparatus and method for reducing hardware complexity by
decreasing a multi-tap size in an equalizer-based receiver of a
mobile communication system.
FIG. 1 is a block diagram illustrating a structure of a receiver in
a mobile communication system according to an exemplary embodiment
of the present invention.
Referring to FIG. 1, the receiver may include an antenna 101, a
receiving unit 103, a matched filter 105, an adaptive multi-tap
segment estimator 107, an equalizer Finite Impulse Response (FIR)
filter 109, a descrambling unit 111, a de-spreading unit 113 and an
equalizer adaptation unit 115.
The matched filter 105 performs matched filtering between a signal
received through the antenna 101 and the receiving unit 103 and a
pre-stored reference signal, and provides the filtered signal to
the adaptive multi-tap segment estimator 107.
The adaptive multi-tap segment estimator 107 de-spreads a signal
whose transmission pattern is predefined, such as a pilot signal.
Thereafter, the adaptive multi-tap segment estimator 107 estimates
a channel by using a correlation with respect to an original data
signal. More particularly, the adaptive multi-tap segment estimator
107 constructed as illustrated in FIG. 2 estimates a multi-tap
located in a position suitable for a signal that has undergone a
multi-path channel delay. The adaptive multi-tap segment estimator
107 will be described below in more detail with reference to FIG.
2.
The equalizer FIR filter 109 performs an equalization operation
according to an equalizer tap gain provided from the equalizer
adaptation unit 115. Thus, the equalizer FIR filter 109 compensates
for a distortion of a multi-path reception signal provided from the
adaptive multi-tap segment estimator 107. Thereafter, the equalizer
FIR filter 109 provides the compensated signal to the descrambling
unit 111.
The descrambling unit 111 descrambles the distortion-compensated
signal and provides the descrambled signal to the de-spreading unit
113. The de-spreading unit 113 de-spreads the signal received from
the descrambling unit 111.
The equalizer adaptation unit 115 determines an equalizer tap gain
by using the multi-tap estimated by the adaptive multi-tap segment
estimator 107 and provides the equalizer tap gain to the equalizer
FIR filter 109.
FIG. 2 is a block diagram illustrating a structure of an adaptive
multi-tap segment estimator of a receiver according to an exemplary
embodiment of the present invention.
Referring to FIG. 2, the adaptive multi-tap segment estimator 107
includes an on-late sampler 201, a multi-tap segment estimator 203,
a chip buffer 205, a channel estimation controller 207, a Pseudo
random Noise (PN) generator 209, a segment controller 211 and a
locking unit 213.
The on-late sampler 201 performs sampling on a double-chip rate
signal provided from the matched filter 105 to generate an
on-sample and a late-sample, each of which is a single-chip rate
signal. Thereafter, the on-late sampler 201 provides the on-sample
and the late-sample to the multi-tap segment estimator 203 and the
chip buffer 205. More particularly, the on-late sampler 201
controls an output of the on-sample and the late-sample according
to a slewing signal input from the channel estimation controller
207.
The multi-tap segment estimator 203 consists of N.sub.seg channel
estimation segments and is a constitutional block for performing
parallel channel estimation on consecutive taps. The multi-tap
segment estimator 203 performs parallel channel estimation on N
consecutive taps having a delay time difference of a half-chip
interval.
The chip buffer 205 is a First Input First Output (FIFO)-type
buffer which sequentially stores the on-sample and the late-sample,
each of which is input from the on-late sampler 201, and
sequentially outputs the on-sample and the late-sample. A data
signal is buffered in the chip buffer 205 for a specific time
period before being output so that the equalizer tap gain of the
equalizer adaptation unit 115 and the data signal of the on-late
sample and the late-sample are input to the equalizer FIR filter
109 at the same time.
The channel estimation controller 207 receives estimated channel
values from the multi-tap segment estimator 203 and analyzes a
channel characteristic. Operations, such as multi-tap energy
determination, multi-tap lock control, Doppler estimation, delay
profile analysis, slewing control, and the like are performed by
the channel estimation controller 207, which will be described
below in more detail with reference to FIG. 5.
The PN generator 209 generates a PN signal including a scrambling
code required for de-spreading, an Orthogonal Variable Spreading
Factor (OVSF) code, an antenna pattern, and the like and provides
the generated signal to the multi-tap segment estimator 203 so that
the multi-tap segment estimator 203 may restore the pilot signal.
More particularly, the PN generator 209 controls an output of the
PN signal according to a slewing signal input from the channel
estimation controller 207.
The segment controller 211 receives information of each tap energy
from the channel estimation controller 207. Thereafter, the segment
controller 211 determines a segment size and a segment count.
Further, the segment controller 211 determines an estimation rate
for each segment and mapping to a hardware segment. Thereafter, the
segment controller 211 provides information regarding the
determined mapping to the channel estimation controller 207. In
addition, the segment controller 211 controls channel estimation
timing of the PN generator 209 and the multi-tap segment estimator
203. An operation of the segment controller 211 will be described
below in more detail with reference to FIG. 6.
FIG. 3 is a block diagram illustrating a structure of a multi-tap
segment estimator according to an exemplary embodiment of the
present invention.
Referring to FIG. 3, the multi-tap segment channel estimator
consists of channel estimation segments 300, 310 and 320 including
N parallel sub-channel estimators 301, 303, 311, 313, 321 and 323,
where N corresponds to a number of multi-taps. The multi-tap
segment channel estimator obtains a channel estimation value for a
multi-tap by using on-samples and the late-samples and a PN signal
(or a PN code). In this case, among the N sub-channel estimators
301, 303, 311, 313, 321 and 323, odd sub-channel estimators 301,
311 and 321 receive on-samples and even sub-channel estimators 303,
313 and 323 receive late-samples. Further, the multi-tap segment
channel estimator includes a plurality of delay buffers 331 and 333
so that a PN signal received from the PN generator 209 is delayed
by a specific chip and is input to each of the sub-channel
estimators 301, 303, 311, 313, 321 and 323. In this case, the delay
buffer 331 and 333 delay the PN signal by a (N/2-1) chip so that
the PN signal is input for each of the two sub-channel estimators
with a time difference corresponding to a one-chip delay time.
The multi-tap segment channel estimator obtains a channel
estimation value for a total of N multi-taps each having a half
chip interval by using the N sub-channel estimators and provides
the channel estimation value to the channel estimation controller
207. Further, the multi-tap segment channel estimator either locks
or unlocks the multiple taps by using a lock/unlock processor 340
and provides resultant multiple taps to the equalizer adaptation
unit 115.
FIG. 4 is a block diagram illustrating a structure of a PN
generator according to an exemplary embodiment of the present
invention.
Referring to FIG. 4, the PN generator includes a PN delay unit for
adjusting a phase of a PN signal so that channel taps of different
regions may be estimated for respective channel estimation
segments. The PN delay unit consists of a PN signal buffer 401 and
an output selector 403.
The PN signal buffer 401 is a buffer for storing the PN signal
provided from the PN generator. Since the PN signal buffer 401
consists of N.sub.max.sub.--.sub.buf buffers, the PN delay unit may
implement phases of 0, 1, . . . , (N.sub.max.sub.--.sub.buf-1)
chips. The output selector 403 is a circuit for mapping
N.sub.max.sub.--.sub.buf buffer values to N.sub.seg outputs.
Mapping information is obtained from an input signal provided from
a channel estimation segment controller. Therefore, the PN delay
unit generates N.sub.seg PN signals each having a different phase
according to the mapping information, and delivers the PN signals
to respective sub-channel segments.
FIG. 5 is a block diagram illustrating a structure of a channel
estimation controller according to an exemplary embodiment of the
present invention.
Referring to FIG. 5, the channel estimation controller includes a
multi-tap energy determiner 501, a multi-tap lock controller 503, a
Doppler estimator 505, a delay profile analyzer 507 and a slewing
controller 509.
The multi-tap energy determiner 501 persistently measures time
average power of a multi-tap channel and provides the measured time
average power to the multi-tap lock controller 503. In this case,
the time average power for the multi-tap channel may be determined
by Equation (1) below.
.function..tau..times..tau..tau..times..function. ##EQU00001##
In Equation (1), P.sub.n(t) denotes a time average power value for
an n.sup.th channel tap, h.sub.n(t) denotes a channel estimation
value for the n.sup.th channel tap, N denotes a number of taps of
the multi-tap segment estimator 203, and N.sub..tau. denotes a
window size for obtaining time average power. When the window size
increases, power control is performed using long-term power. When
the window size decreases, power control is performed using
short-term power. For example, if the window size is 1, power
control is performed using only instantaneous power.
The multi-tap lock controller 503 obtains a sum of respective
channel-taps' time average power values determined by the multi-tap
energy determiner 501 as expressed by Equation (2) below.
Thereafter, the multi-tap lock controller 503 determines a lock
threshold as expressed by Equation (3) below by using the sum of
the time average power values.
Equation (2) below shows a power sum at a time t.
.function..times..function. ##EQU00002##
In Equation (2), P.sub.tot(t) denotes a total sum of time average
power at a time t, and P.sub.n(t) denotes a time average power
value for an n.sup.th channel tap.
Equation (3) below shows a lock threshold.
T.sub.L=P.sub.tot(t)/T.sub..alpha. (3)
In Equation (3), T.sub.L denotes a lock threshold, P.sub.tot(t)
denotes a total sum of time average power at a time t, and
T.sub..alpha. denotes a coefficient of the lock threshold. The
coefficient of the lock threshold has a different magnitude
according to a Signal to Interference and Noise Ratio (SINR). That
is, in an environment where the SINR is high, a value estimated by
the sub-channel estimator is relatively accurate. Thus, the
magnitude of the lock threshold is decreased to lock taps as many
as possible. In an environment where the SINR is low, the value
estimated by the sub-channel estimator includes relatively great
noise. Thus, the lock threshold is increased to unlock taps as many
as possible.
The multi-tap lock controller 503 determines whether each multi-tap
is locked or unlocked according to Equation (4) below, and provides
the determined result to the multi-tap segment estimator 203.
.times..times..times..times.>.times. ##EQU00003##
In Equation (4), 1 implies that a tap is locked and 0 implies that
the tap is unlocked.
The Doppler estimator 505 determines a time-correlation of a
multi-tap channel. Thereafter, the Doppler estimator 505 estimates
a movement speed of the receiver according to the determined
time-correlation. The result obtained by the Doppler estimator 505
is used to generate a parameter for determining a filter
coefficient of a sub-channel estimator filter and a convergence
rate of an equalizer.
The delay profile analyzer 507 analyzes a multi-path characteristic
of a reception channel by using the estimated multi-tap channel
values. When a multi-path delay profile moves over time or is
located on one side of the multi-tap of the channel estimator, the
slewing control block generates a slewing signal by performing
slewing on multi-paths so that the multi-path delay profile is
properly distributed in a center portion of the multi-tap of the
channel estimator. In this manner, the slewing control block
controls the on-late sampler and the PN generator.
The slewing controller 509 controls the on-late sampler and the PN
generator in such a manner that, when the multi-path delay profile
moves over time or is located in one side of the multi-tap of the
channel estimator, a slewing signal is generated by performing
slewing on multi-paths so that the multi-path delay profile is
properly distributed in a center portion of the multi-tap of the
channel estimator.
FIG. 6 is a block diagram illustrating a structure of a segment
controller according to an exemplary embodiment of the present
invention.
Referring to FIG. 6, the segment controller includes a segment size
decision unit 601, a multi-tap block energy analyzer 603, a
multi-tap segmentation unit 605 and a segment delay control unit
607. The segment size decision unit 601 analyzes a delay spread of
a channel tap to determine a segment size N.sub.sub. By using a
segment count N.sub.seg and a total number N of sub-channel
estimators (where N=N.sub.seg.times.N.sub.sub), the segment size
decision unit 601 may obtain the segment size N.sub.sub.
The multi-tap block energy analyzer 603 determines a block sum of
energy in each segment block. The energy block sum of each segment
and a Doppler level are used by the multi-tap segmentation unit 605
to obtain an estimation frequency of each segment and to perform
mapping to a hardware segment. The mapping information is delivered
to the channel estimation controller. By using determined segment
mapping information, the segment delay control unit 607 generates a
signal for controlling a PN delay unit and a channel estimation
segment in every channel estimation period.
FIG. 7 is a flowchart illustrating a multi-tap lock control process
of a channel estimation controller in a receiver according to an
exemplary embodiment of the present invention.
Referring to FIG. 7, in step 701, the channel estimation controller
determines energy of each multi-channel tap, i.e., time average
power, as expressed by Equation (1) above. In step 703, the channel
estimation controller determines a total sum of the time average
power and a lock threshold depending on the total sum thereof as
expressed by Equations (2) and (3) above.
In step 705, the channel estimation controller determines whether
each multi-tap is locked as expressed by Equation (4) above. In
step 707, the channel estimation controller locks or unlocks each
multi-tap and provides a resultant multi-tap to an equalizer
adaptation unit. Thereafter, the procedure ends.
FIG. 8 is a flowchart illustrating a slewing process using a
movement average in a receiver according to an exemplary embodiment
of the present invention.
Referring to FIG. 8, in step 801, the receiver determines energy of
each multi-channel tap, i.e., time average power, as expressed by
Equation (1) above. In step 803, the receiver analyzes a delay
profile of a multi-path channel by using a movement average
mechanism as expressed by Equation (2) above. In step 805, the
receiver determines a maximum power position as expressed by
Equation (3) above.
In step 807, the receiver compares the maximum power position with
a reference position.
If the maximum power position is less than the reference position,
in step 809, the receiver performs negative slewing. If the maximum
power position is greater than the reference position, in step 813,
the receiver performs positive slewing. If the maximum power
position is equal to the reference position, in step 811, the
receiver determines not to perform slewing. Then, the procedure
proceeds to step 815.
In step 815, the receiver controls locking of the multi-tap.
Thereafter, the procedure ends.
FIG. 9 is a flowchart illustrating a segment control process of a
receiver according to an exemplary embodiment of the present
invention.
Referring to FIG. 9, the receiver determines time average power for
each channel tap in step 901, and then determines a delay spread
value in step 903.
The time average power for each channel tap is determined by a
channel estimation controller of the receiver. The delay spread
value may be determined by using a time average energy value
provided from the channel estimation controller. In addition, the
delay spread value is defined as a Root Mean Square (RMS) delay
spread, that is, a square root of a second central moment of a
power delay profile.
In step 905, the receiver determines a segment size by using
Equation (5) below. In step 907, the receiver determines energy of
each segment block. N.sub.sub=f(delay_spread) (5)
In Equation (5), f(.cndot.) denotes a simple increment function.
The greater the delay spread value, the greater the segment size.
The smaller the delay spread value, the smaller the segment size.
This is because, when the delay spread value is great, energy of a
received signal is widely distributed and thus a size of a segment
requiring fast channel estimation needs to be large. Whereas when
the delay spread value is small, the energy of the received signal
is narrowly distributed and thus the size of the segment requiring
fast channel estimation needs to be small. A function of
determining a segment size may be implemented in a format of a
table having several levels.
In step 909, by using Equation (6) below, the receiver determines a
sum of each segment block's energy determined in step 907.
.times..di-elect cons..times..function. ##EQU00004##
In Equation (6), N.sub.sub may be determined by using a segment
count N.sub.seg and a total number N of sub-channel estimators
(where N=N.sub.seg.times.N.sub.sub). P.sub.j(t) denotes time
average energy of a j.sup.th tap at a time t. A block sum of a
segment S.sub.i may be obtained by averaging time average energy of
taps belonging to the segment S.sub.i.
After determining an energy sum of each segment block as described
above, in step 911, the receiver determines a channel estimation
frequency or a channel estimation rate by using the determined
segment blocks' energy sum and a Doppler level. The Doppler level
may be provided by the channel estimation controller.
In step 913, the receiver allocates each segment to the channel
estimator. Thereafter, the procedure ends.
FIG. 10 is a flowchart illustrating a process of determining a
channel estimation rate in a receiver according to an exemplary
embodiment of the present invention.
Referring to FIG. 10, in step 1001, the receiver compares energy of
an I.sup.th segment with a threshold for determining a channel
estimation rate. In step 1003, the receiver determines whether the
energy of the I.sup.th segment is greater than a threshold for a
maximum rate.
If it is determined in step 1003 that the segment energy is greater
than or equal to the threshold for the maximum rate, in step 1009,
the receiver performs channel estimation with the maximum rate.
Otherwise, if it is determined in step 1003 that the segment energy
is less than the threshold for the maximum rate, in step 1005, the
receiver determines whether the energy of the Ith segment is
greater than a threshold for a minimum rate.
If it is determined in step 1005 that the segment energy is greater
than or equal to the threshold for the minimum rate, that is, if a
channel estimation criterion of using an optimal rate is satisfied,
in step 1013, the receiver performs channel estimation with the
minimum rate.
Otherwise, if it is determined in step 1005 that the segment energy
is less than the threshold for the minimum rate, that is, if the
segment energy does not satisfy both the threshold for the maximum
rate and the threshold for the minimum rate, in step 1007, the
receiver continues to perform the process of determining the
channel estimation rate.
In step 1007, the receiver determines whether a Doppler level is
greater than or equal to a threshold for a maximum rate. If the
Doppler level is greater than or equal to the threshold for the
maximum rate, the procedure proceeds to step 1009. Otherwise, if
the Doppler level is less than the threshold for the maximum rate,
in step 1011, the receiver performs channel estimation with a half
rate.
In step 1015, the receiver determines whether a channel frequency
is determined for all segments.
If it is determined in step 1015 that the channel frequency is not
determined for all segments, in step 1017, the receiver increments
a segment order by 1.
Otherwise, if it is determined in step 1015 that the channel
frequency is determined for all segments, the procedure ends.
FIG. 11 is a flowchart illustrating a process of performing a
channel search mode in a receiver according to an exemplary
embodiment of the present invention.
Referring to FIG. 11, in step 1101, the receiver determines a
channel estimation frequency by using segment blocks' energy sum
and a Doppler level. Step 1101 corresponds to the step 911 of FIG.
9.
In step 1103, the receiver determines a hardware occupancy rate
required for channel estimation of the receiver. The receiver may
determine the hardware occupancy rate by using Equation (7)
below.
.times..times..function. ##EQU00005##
In Equation (7), r(i) denotes a segment time occupancy rate for an
i.sup.th segment and is equal to a segment channel estimation rate.
Accordingly, r(i)=1 if estimation is performed with a maximum
estimation rate, and r(i)=0.5 if estimation is performed with a
half rate.
If an occupancy rate is 1 for all hardware segments, it implies
that estimation is performed for all hardware segments with a
maximum rate. If the occupancy rate is less than 1 for all hardware
segments, it implies that there is an unused hardware segment.
In step 1105, the receiver determines whether a hardware occupancy
rate is less than a threshold for performing a search mode in step
1107. If it is determined that the hardware occupancy rate is less
than the threshold, segments with a low estimation rate share
hardware segments to reduce hardware size in an initial design
process and to reduce power consumed during operation, and unused
hardware segments are used in a search mode for a neighbor tap
region or another channel.
In step 1107, the search mode searches for a neighbor channel tap
by regulating a PN phase, and may also be used when implementing a
PN signal with a different code IDentification (ID).
The reason of comparing the hardware occupancy rate with the
threshold for performing the search mode as described in step 1105
is to compare accuracy of the search mode and complexity of control
so that the search mode is not operated when the occupancy rate is
less than 1 and the search mode is operated only when the occupancy
rate is less than or equal to a specific level.
FIGS. 12A-12B illustrate a performance difference between a
conventional receiver and a receiver according to an exemplary
embodiment of the present invention.
FIG. 12A illustrates a performance of the conventional
receiver.
Referring to FIG. 12A, the conventional receiver 1201 processes a
received signal in such a manner that a channel estimator with a
long tap persistently performs channel estimation with a constant
rate all the time, and an equalizer locks a region having high tap
energy and unlocks a region having low tap energy. As illustrated
in FIG. 12A, disadvantageously, the channel estimator has to be
designed to have a sufficiently long tap and all taps have to
operate all the time.
FIG. 12B illustrates a performance of a receiver according to an
exemplary embodiment of the present invention.
Referring to FIG. 12B, an operational performance of a receiver
1202 is illustrated in a condition where a search mode is not
provided. A channel tap region to be estimated is divided into four
segments. According to a segment energy block sum, a segment 1 and
a segment 2 are assigned with full rate estimation and a segment 0
and a segment 3 are assigned with half rate estimation. As a
result, the segment 1 and the segment 2 always allocate hardware
segments (i.e., full use), and the segment 0 and the segment 3
share a Hardware (HW) segment 0. Therefore, a hardware occupancy
rate is 0.75, and an HW segment 3 is unused. Thereby, power
consumption is reduced.
FIG. 12C illustrates a performance of a receiver according to an
exemplary embodiment of the present invention.
Referring to FIG. 12C, an operational performance of a receiver
1203 is illustrated in a condition where a search mode is provided.
An operation of allocating segments of a channel tap to hardware
segments is identical to an operation used in the absence of the
search mode. Likewise, a hardware occupancy rate is 0.75, and even
if an HW segment 3 is not used, a reception performance does not
deteriorate. However, the HW segment 3 unused in the search mode is
allocated for a neighbor channel search. As illustrated in FIG.
12C, energy of a neighbor channel is detected. Therefore, traffic
performance may be improved when such information is used in
advance.
According to exemplary embodiments of the present invention,
hardware complexity is reduced by decreasing a multi-tap size in an
equalizer-based receiver of a mobile communication system. A
channel estimation rate is determined by dividing the multi-tap
size into a plurality of segments, and thus hardware size and power
consumption of the receiver may be decreased.
While the present invention has been shown and described with
reference to certain exemplary embodiments thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the present invention as defined by the appended
claims and their equivalents.
* * * * *